Specific binding assays are test methods for detecting the presence or amount of a substance and are based on the specific recognition and binding together of specific binding partners. Immunoassays are an example of a specific binding assay in which an antibody binds to a particular protein or compound. In this example an antibody is a member of a specific binding pair member. Nucleic acid binding assays are another type in which complementary nucleic acid strands are the specific binding pair. Specific binding assays constitute a broad and growing field of technology that enable the accurate detection of disease states, infectious organisms and drugs of abuse. Much work has been devoted over the past few decades to devise assays and assay methodology having the required sensitivity, dynamic range, robustness, broad applicability and suitability to automation. These methods can be grouped broadly into two categories.
Homogeneous methods utilize an analyte-specific binding reaction to modulate or create a detectable signal without requiring a separation step between analyte-specific and analyte non-specific reactants. Heterogeneous formats rely on physical separation of analyte-bound and free (not bound to analyte) detectably labeled specific binding partners. Separation typically requires that critical reactants be immobilized onto some type of solid substrate so that some type of physical process can be employed, e.g. filtration, settling, agglomeration or magnetic separation, and typically also require wash steps to remove the free detectably labeled specific binding partners.
Assay methods relying on producing a chemiluminescent signal and relating it to the amount of an analyte have experienced increasing use. Such methods can be performed with relatively simple instruments yet display good analytical characteristics. In particular, methods employing an enzyme-labeled specific binding partner for the analyte and a chemiluminescent enzyme substrate for detection have found widespread use. Common label enzymes include alkaline phosphatase and horseradish peroxidase.
U.S. Pat. No. 6,911,305 discloses a method of detecting polynucleotide analytes bound to a sensitizer or sensitizer-labeled probe on a first film. The film is contacted with a second film bearing an immobilized chemiluminescent precursor. Exciting the sensitizer in the sandwiched films produces singlet oxygen which reacts with the chemiluminescent precursor to produce a triggerable chemiluminescent compound on the second film. The triggerable chemiluminescent compound is reacted with a reagent to generate chemiluminescence on the second film for detecting the analyte. These methods do not rely on the specific binding reaction for bringing the reactants into contact; rather the second film serves as a reagent delivery device.
U.S. Pat. No. 6,406,913 discloses assay methods comprising treating a medium suspected of containing an analyte under conditions such that the analyte causes a photosensitizer and a chemiluminescent compound to come into close proximity. The photosensitizer generates singlet oxygen when irradiated with a light source; the singlet oxygen diffuses through a solution to and activates the chemiluminescent compound when it is in close proximity. The activated chemiluminescent compound subsequently produces light. The amount of light produced is related to the amount of analyte in the medium. In one embodiment, at least one of the photosensitizer or the chemiluminescent compound is associated with a suspendible particle, and a specific binding pair member is bound thereto
U.S. patent application publications US20070264664 and US20070264665 disclose assay methodology for performing specific binding pair assays involving reaction of immobilized chemiluminescent compounds with activator compounds brought into a reactive configuration by virtue of the specific binding reaction. No separation or removal of the excess unbound chemiluminescent compound or activator is required. These assay formats provide superior operational convenience and flexibility in automation compared to prior art assay techniques. Despite these advantages, additional improvements in assay design and performance remain a goal of assay developers. The assay methods of the present disclosure address these needs by providing simple assay methods of improved sensitivity.